1. Field of the Invention
This invention relates to electrical connectors for thin film devices (i.e., devices having one or more thin film electrodes in which the thickness of each electrode is less than about, e.g., 2 .mu.m) having an electrically responsive layer designed to deliver electric current from a power supply to an electrode.
2. Description of the Related Art
Many types of thin film devices having an electrically responsive layer are known. They include thin film electro-optical devices in which the optical properties of the electrically responsive layer change. Electric current is supplied to the device by means of a connector that delivers current from an external power supply to at least one electrode in contact with the electrically responsive layer.
One example of a thin film electro-optical device is an electrochromic device. Such a device relies upon a reversible chemical reaction that takes place in the electrically responsive layer upon application of current to cause a change in optical properties.
A second example is a display device containing a layer of electrically responsive liquid crystal material. Application of an electric field causes the alignment, and thus the optical properties, of the liquid crystal layer to change.
A third example is the so-called Nematic Curvilinear Aligned Phase ("NCAP") device described, e.g., in Fergason, U.S. Pat. No. 4,435,047, hereby incorporated by reference. These devices include an electrically responsive liquid crystal layer in which nematic liquid crystal material is encapsulated in a polymer matrix. The encapsulated material is prepared by combining the liquid crystal material with the polymer matrix in the form of an aqueous emulsion, and then casting a film from the emulsion. These devices are relatively translucent in the absence of an electric field due to light scattering, but are relatively transparent upon application of a field.
A fourth example of electro-optical device is the Polymer-Dispersed Liquid Crystal ("PDLC") device described, e.g., in Doane et al., U.S. Pat. No. 4,688,900, hereby incorporated by reference. These devices include an electrically responsive liquid crystal layer in which liquid crystal droplets are dispersed throughout a polymer matrix. The liquid crystal layer is prepared by combining the liquid crystal material with a polymerizable matrix precursor and then subjecting the mixture to polymerization conditions. Polymerization causes phase separation of the liquid crystal material, resulting in the formation of liquid crystal droplets dispersed throughout the polymerized matrix. Like the NCAP devices, these PDLC devices are translucent in the absence of an electric field due to light scattering and become transparent upon application of the field.
Reverse mode PDLC devices are also known. These devices are transparent in the absence of an electric field and become translucent upon application of the field.
A fifth example is an electroluminescent device. In such a device, the electrically responsive layer consists of electrically responsive particles (e.g., zinc sulfide) that luminesce upon application of current.
In all of these devices, it is necessary to establish an electrical connection between the electrode and the power supply. One example of such a connector is shown in Mori et al., U.S. Pat. No. 4,956,031. Mori describes an electroluminescent device having an "auxiliary electrode" in the form of a long narrow strip. The purpose of the "auxiliary electrode" is to distribute voltage over the entire electroluminescent layer and to provide a connection to the power supply. It consists of a conductive metal layer sandwiched between an insulating layer and an electrically conductive adhesive. The "auxiliary electrode," in turn, is sandwiched between the electroluminescent layer and the electrode of the device such that the insulating layer contacts one face of the electroluminescent layer, while the adhesive contacts one face of the electrode. The "auxiliary electrode" is not inserted into the electroluminescent layer.
The connection between the power supply and electrode is often the source of failure in thin film devices, resulting in melting and subsequent arcing of the electrode layer. There is a need, therefore, for a compact electrical connector that provides a reliable connection between the power supply and electrode of such thin film devices.